Time for me to toss my hat into the ring, but mind that this is a preliminary sketch and a rough one at that. My concept: sloth. Sloths are dark and malevolent creatures, evil beyond compare and excellent for this concept. Just look at their malicious grin, those beady hateful eyes, those enormous fleshripping claws, and you know the truth. You know there is a reason they are the name of a deadly sin.
Also, they grow algae and mold in their fur, so grass type.
A depiction of murder sloth in a more familiar context.